A motor vehicle, such as a mining truck, can be equipped with a liquefied natural gas (LNG) pump that fuels an engine of the truck. When the truck is in use, and the pump is active, the pump pushes LNG from an associated tank into the engine. During periods of nonuse, LNG is no longer drawn through the pump.
LNG is a fuel that has been cooled to about −160° C. Therefore, a pump that has been inactive for an extended period of time is devoid of this cold fuel and warms to ambient temperatures. The pump is then required to be primed, and thereby cooled, before the engine may be started. Priming an LNG pump traditionally involves flooding the pump with LNG or a separate coolant to cool the pump. However, introducing LNG to a warm pump can cause the LNG to boil during the priming process. This boiling releases an unwanted gaseous build-up at the pump inlet or in the pump itself, causing it to be “vapor locked.” The pump then requires additional cooling time to liquify the vapor before the pump is ready to perform. Introducing a separate coolant involves the extra step of removing the coolant from the system and disposing of it before the LNG can be pumped from the tank.
One attempt to avoid gaseous build-up in an LNG pump during priming is to connect the pump to a vapor dome collector that sits above the pump. In this configuration, any gaseous release naturally flows up and into the vapor dome collector, allowing only LNG to flow down and into the pump. The gas vapor may then be directed back into the tank, securely away from the pump. One such system is described in U.S. Pat. No. 5,431,546 (the '546 patent) by Rhoades, issued on Jul. 11, 1995.
Although the '546 patent may allow the pump to be primed without risk of vapor lock, the system may be wasteful, expensive, and incapable of safely venting. In particular, when using the system disclosed in the '546 patent, an amount of LNG may be boiled and converted into gas, which is of no use when priming a pump. Additionally, LNG may be expensive for use as a coolant, especially when LNG is boiled and therefore wasted. LNG released into the atmosphere, from the vapor dome collector and/or tank, may constitute an environmental and safety hazard. LNG may evaporate and form a flammable vapor cloud that can explode. Therefore, a user may not want to vent LNG into the atmosphere, especially when working in a shop or other closed environment.
The disclosed system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.